1. Field of the Invention
The present invention relates to a dry etching method and method of manufacturing a semiconductor device, and more particularly to a dry etching method for forming a semiconductor device structure on a semiconductor wafer.
2. Description of the Related Art
In a semiconductor device, a silicon oxide (hereinafter referred to SiO2) layer is widely used as an interlayer layer where a contact hole (via hole), a wiring groove, and the like is formed by a dry etching process.
In the dry etching process, as a etching stopper film (film for selectively stopping the progress of etching in a position thereof) used for an etching depth to be uniform, a silicon nitride (hereinafter referred to Si3N4) film is most frequently used. This is because the film is the most superior film as the etching stopper film of the insulating layer in view of stability as the film, compatibility with the SiO2 layer, heat resistance, insulating property, and other general properties.
Moreover, a gas for general use in SiO2 etching at present is a gas mainly comprising CxFy (x and y are positive integers). In addition, argon (Ar), oxygen (O2), carbon monoxide (CO) and the like may be added to this main gas as occasion demands.
As described above, Si3N4 is most frequently used as the etching stopper of the insulating layer, but sufficiently high selection property can not be obtained in an SiO2 etching process which is generally performed at present.
There are two reasons for this with regard to a semiconductor device structure. The first reason is that the contact hole used in recent years is remarkably high in aspect ratio, a deposition component does not easily enter a hole bottom part, and sufficient protection effect is not obtained. The second reason is that Si3N4 has the insulating property, but dielectric constant of Si3N4 is higher than that of SiO2, and therefore, Si3N4 remaining outside the contact hole as a part of the insulating layer must be as thin as possible (about 50 nm). Consequently, the film thickness of the Si3N4 as a etching stopper film becomes inevitably thin as about 50 nm, and therefore, the required selection property is a remarkably high value such as the order of 50 to 100. By these reasons, as a selection ratio to Si3N4 in insulation layer etching, a substantially infinite selection ratio is required, but it is remarkably difficult to achieve the ratio in a current etching method.
A reason why the high selection property cannot be obtained with respect to Si3N4 in the conventional etching method in which the CxFy gas is used as the main gas is as follows. When an active species of the gas contacts Si3N4, first C extracts N on a surface, F attacks freed Si and the etching supposedly proceeds in this pattern. Since both (CN)x and SiF4 are high vapor pressure materials, on occurrence of a reaction the etching proceeds.
Wherefore, one object of the present invention is to provide an effective dry etching method, which solves the aforementioned related-art problems.
Another object of the present invention is to provide a method of manufacturing a semiconductor device using the effective dry etching method.
According to the present invention, there is provided a dry etching method which comprises a step of etching an insulating layer of a semiconductor device structure using a silicon nitride represented by Si3N4 as an etching stopper under an etching gas atmosphere. The etching gas includes a gas containing iodine in a molecule. The insulating layer may be a silicon oxide represented by SiO2 layer, a fluorine-containing silicon oxide layer, or an organic SOG layer or another silicon oxide insulating layer. Additionally, a mixing ratio (I/C) of iodine to carbon in the etching gas, that is, a ratio of number (quantity) of iodine atoms to number (quantity) of carbon atoms in the etching gas is 0.3xe2x89xa6(I/C)xe2x89xa61.5, that is, the ratio (I/C) is 0.3 or more, and 1.5 or less. Here, the iodine-containing gas can be an HI gas or a gas having a constitution of CxHyIz (x, y and z are positive integers).
According to another aspect of the present invention, there is provided a dry etching method which comprises a step of etching an insulating layer of a semiconductor device structure using a silicon nitride film represented by Si3N4 as an etching stopper under an etching gas atmosphere. The etching gas includes a gas containing chlorine or bromine in a molecule. The insulating layer may be a silicon oxide represented by SiO2 layer, a fluorine-containing silicon oxide layer, or an organic SOG layer or another silicon oxide insulating layer. Additionally, a mixing ratio (Cl (or Br)/C) of chlorine or bromine to carbon in the etching gas is 0.3xe2x89xa6(Cl (or Br)/C)xe2x89xa61.5. That is, a ratio of number (quantity) of chlorine atoms or bromine atoms to number (quantity) of carbon atoms in the etching gas is 0.3 or more, and 1.5 or less. Here, the gas containing chlorine or bromine can be a Cl2 gas, an HCl gas, a gas having a constitution of CxHyClz (x, y and z are positive integers), a gas having a constitution of CxClz (x, and z are positive integers), for example, CCl4, a Br2 gas, an HBr gas, or a gas having a constitution of CxHyBrz (x, y and z are positive integers)
According to further aspect of the present invention, there is provided a method of manufacturing a semiconductor device which comprises steps of forming a wiring layer on a semiconductor substrate via an insulator, forming a silicon nitride film represented by Si3N4 on the wiring layer, forming an insulating layer on the silicon nitride film, and forming a contact hole in the insulating layer by a dry etching method. The dry etching method includes a step of etching the insulating layer by using the silicon nitride film as an etching stopper under an etching gas atmosphere. The etching gas includes a gas containing iodine, chlorine or bromine in a molecule, and a mixing ratio ((I, Cl or Br)/C) of iodine, chlorine or bromine to carbon in the etching gas is 0.3 or more, and 1.5 or less.
According to yet further aspect of the present invention, there is provided a method of manufacturing a semiconductor device which comprises steps of forming a pair of gate electrode structures on a semiconductor substrate via gate insulating films, covering the gate electrode structures and a space between the gate electrode structures with a silicon nitride film represented by Si3N4 continuously, forming an insulating layer on the silicon nitride film, and forming a contact hole in the insulating layer between the gate electrode structures by a dry etching method. The dry etching method includes a step of etching the insulating layer by using the silicon nitride represented by Si3N4 film as an etching stopper under an etching gas atmosphere. The etching gas includes a gas containing iodine, chlorine or bromine in a molecule, and a mixing ratio ((I, Cl or Br)/C) of iodine, chlorine or bromine to carbon in the etching gas is 0.3 or more, and 1.5 or less.
Furthermore, the aforementioned etching method is preferably used when a contact hole with an aspect ratio of 20 or less is formed in the insulating layer.
In this case, etching is performed by the etching gas from the surface of the insulating layer to reach Si3N4 so that the contact hole can be formed in the insulating layer. Alternatively, in a two-step etching method which comprises performing etching from the surface of the insulating layer with a first etching gas to form an upper part of the contact hole, and subsequently performing the etching with a second etching gas until Si3N4 is reached to form a lower part of the contact hole; the aforementioned etching gas including iodine, chlorine or bromine can be used as the second etching gas.
According to the dry etching method of the present invention, iodine contained in the etching gas forms CNI, which is a low vapor pressure material on Si3N4, and inhibits the etching of the Si3N4. Also, when the chlorine or bromine-containing gas is used, CNCl or CNBr, that is, a relatively low vapor pressure material is formed to inhibit the etching of the Si3N4.
In either case, since no low vapor pressure material is generated on SiO2 as the material to be etched, SiOF whose dielectric constant is lowered by containing fluorine in silicon oxide, or organic SOG, a high etching rate can be obtained.
Moreover, when a CxHyFz (x, y and z are positive integers) gas used in recent years is added, NH3 with a higher vapor pressure is generated, and it is therefore difficult to keep a high selection property with respect to Si3N4. However, even in this case, when an iodine-containing gas is used, NH4I with a low vapor pressure is formed to inhibit the etching of the Si3N4 film.
The reason why the ratio (I/C) of iodine to carbon in the etching gas is set in a range of 0.3xe2x89xa6(I/C)xe2x89xa61.5 is that an effect of the range includes dependence on an aspect ratio, and with a larger aspect ratio the I/C ratio needs to be set to be high. Specifically, according to various experiments/inspections by the present inventors, when flat and large patterns such as a pad pattern are etched, a sufficient etching inhibition effect is obtained at I/C=0.3. However, in order to obtain a sufficient etching inhibition effect in Si3N4 in a contact hole bottom part with an aspect ratio of 20 (e.g., hole diameter of 0.15 xcexcm/depth of 3.0 xcexcm), which is a largest aspect ratio in a presently used semiconductor device, I/C=1.5 is necessary. Moreover, it has been confirmed by the experiments that the etching inhibition effect depends on the aspect ratio rather than on the hole diameter. This respect will be described in an embodiment.
Furthermore, it has been confirmed that even when instead of the iodine-containing gas the gas containing chlorine or bromine as the same halogen element is used, the similar action/effect can be produced.